As packaging density of microelectronic devices increases with technology developments, manufacturers are continually shrinking the sizes of microelectronic devices to satisfy increasing demand for smaller electronic devices. Another trend in modern microelectronic devices is the increasing use of higher power consumption circuits, such as in a modern CPU chip. In order to accommodate the more densely packaged and the higher power consumption microelectronic devices, the heat dissipation property of a conventional flip chip package (e.g., ball grid array and land grid array) needs be improved.
A heat sink, sometimes called a heat spreader, normally made of a higher thermal conductivity material such as copper has been used to fulfill the need for improving heat dissipation in flip chip packages. Although copper, with its high thermal conductivity is a common solution for a lid of the heat spreader, there exists a coefficient of thermal expansion (CTE) mismatch between the copper lid and the low CTE ceramic substrate of the flip chip package. A CTE mismatch between these two materials induces a stress concentration on the adhesive region between the heat spreader lid and the ceramic substrate leading to a risk of delamination of the heat spreader lid from the substrate. To resolve the CTE mismatch problem, low CTE metal or metal/ceramic composite materials such as copper tungsten (CuW) or aluminum-silicon-carbide (AlSiC) have been proposed and used; however, the thermal performance of these materials is not as good as copper because they have comparatively low thermal conductivity.
The increased use of more densely packaged microelectronic devices, high powered CPUs that lead to localized areas on the chip having relatively high heat generation (e.g., “hot spots”), delicate extreme low k (ELK) dielectric layers, and lead free bumps, have all increased the risk of cracks in the dielectric layers and delamination between the heat spreader and the substrate. Accordingly, a heat spreader having not only enhanced thermal dissipation but also one being able to resolve the CTE mismatch issue is becoming ever more crucial.
Upon reading the following detailed description, it will become more apparent that there is a need for a thermally enhanced heat spreader in advanced IC packaging such as flip chip that avoids the delamination and CTE mismatch concerns associated with conventional heat spreaders.